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Geology
science pursuing an understanding of Earth
Physical Geology
examines materials composing Earth to understand processes that operate beneath and on its surface
Aspects of geology affecting people
(1)Natural Hazards
[flood, earthquake, volcano, landslides]

(2)Natural Resources
[oil & gas, metals, coal/uranium, gravel/sand, H20]
Geologic time scale
-Billions of years

-reoccurance normally longer than human life span

-100 million yrs ago = recent

-rock sample 10 million yrs old = young
Science assumes...
the natural world is consistent and predictable
Goal of science...
discover patterns in nature to make predictions from
Science collects facts through..
observation & measurement
The Earth system is powered by
(1) The Sun
---drives external processes [climate, erosion]


(2)Earth's interior.

-a-heat remaining from its formation
-b-heat still generated by radioactive decay
(powers the interal processes that make volcanos/earthquakes/mountains)


-Earth convects like a boiling pot exchanging heat from inside to surface
plate tectonics are driven by
convection of the mantle
Greater size of planet = slower loss of heat

[relating to earth/mars?]
Earth is still shedding heat

Mars = smaller = already lost internal heat
=never convected = no plate techtonics = 1 LARGE volcano rather than multiple small volcanos
3 main rock types
IGNEOUS

SEDIMENTARY

METAMORPHIC
The Rock Cycle shows:
the cycles in which rocks change into other rocks

shows processes that materials change on the surface & inside of earth
Nebular Hypothesis
bodies in solar system evolved from enourmous rotating cloud [the solar nebula] made of gasses and dust grains
--solar nebula slowly contracted due to gravity
---rotated faster
---cload assumed disk shape w/concentration @ center (the pre-sun)
---gravitational energy converted to thermal energy [sun formed]
---cooling of cloud caused rocky material to condense into solid particles
---collisions caused particles to grow into planets
Earth is ___ yrs old
4.5 billion
Geologic time scale made by:
first fossils

then given actual numbers using radioactive dating
Origin of Earth
1. big bang
(larg explosion sending all matter of universe flying outward at high speed)

2. debris (mostly H and He) colled/condensed into first stars/galaxies
---in our galaxy=milky way=our solar system formed

3. Nebular Hypothesis

*earth & other planets formed from same material as sun

4. Layered structure of earth developed

5. dense material moves to center of earth... light material stays at shallow levels
Earth's Layers
-iron rich core
-the mantle (largest layer)
-thin primitive crust
Formation of Earth's core
-intense heating due to radioactive decay
-causes iron and nickel to melt
-dense liquid metal sank toward center of planet
Formation of Earth's Mantle
-same early heating formed buoyant masses of molten rock
-light molten rock rose toward surface
-solidified to form primitive crust
*enriched in O2
Earth's internal layers can be defined by:
1) chemical composition

2) physical properties
Earth's Layers Defined by Chemical Composition:
1)Crust
2)Mantle
3)Core
Earth's Layers Defined by Physical Properties
1) Lithosphere (crust & uppermost mantle)
[acts like brittle solid]
2) Astehnosphere
[acts like plastic solid]
3) Mesosphere (lower mantle)
4) Core (outer & Inner)
Chemical Comp. of Crust
1)oceanic crust
-composed of igneous rock (BASALT)

2)continental crust
-many rock types (upper=mostly granitic, lower=mostly basalt)
Chemical Comp. of Mantle
-82% of earth's volume
-uppermost mantle=mostly peridotite
(@ greater depth peridotite has more compact crystalline structure & greater density)
Chemical Comp. of Core
-iron nickel alloy (mix)
-minor amts of O2, silicon, & sulfur (form compounds easily w/ iron)
Physical Prop. of Lithosphere
-consists of crust and uppermost mantle
-cool rigid shell (cool=strong=rigid)
Physical Prop. of Asthenosphere
-in upper mantle
-soft, comparatively weak to lithosphere
-has a small amt of melting
-mechanically detached from lithosphere = *the lithosphere can move independently of asthenosphere*
-acts like plastic solid
Physical Prop. of Lower Mantle (mesosphere)
-increased pressure counteracts high temps
=rocks gradually strengthen with depth
-rigid strong, but still hot and capable of gradual flow
Physical Prop. of Core
1)outer core
- liquid layer
- convective flow of metallic iron
=generates magnetic field

2)inner core
-high temps but stronger than outer core due to immense pressure
-behaves like a solid
Moon
Made up of same rocks as Earth

About the same age as Earth
Formation of Moon
-impact of mars-size planet w/early earth
-ejected debris entered orbit around earth
-condensed to form moon
*ejecterd material mostly iron-poor mantle & crustal rocks == small iron core on moon
Terrestrial v Jovian planets
Terrestrial:
-small
-inner planets
-Mercury Venus Earth Mars
-rocky
-minor ice
-minor gas
== meager atmospheres

Jovian:
-Large
-Outer planets
-Jupiter, Saturn, Uranus, Neptune
-gases (hydrogen, helium)
=thick atmospheres
-ices (water, amonia, methane)
Escape Velocity
the speed a gas molecule can evaporate from a planet

-bigger planets = higher escape velocities = difficult for gas to evaporate from them

-moon unable to hold gases = lack of atmosphere
====no weatering/erosion
Earth has less craters than moon
bc of Earth's greater atmosphere

friction [in earth's atmosphere] burns up small debris before it hits the ground
ejecta
ejected material from crater when meteoroid strikes
Earth v. Mars
both terrestrial planets

Mars:
-smaller
-atmosphere is 1/100 density of earth's atmosphere
-polar caps = water ice covered by frozen carbon dioxide
-lost heat early in history
====mantle never convected
====no plate tectonics
====all heat lost through one place
====gigantic volcano [ex. mons olympus]
-lost magnetic field and atmosphere
====less erosion
Reasons for Mars' giant volcanos
-lost heat early in history
[no plate tectonics=heat lost in one place]

-smaller than earth
[less gravity=longer til gravity pulls down volcanos]
Where do we land on mars?
@ low elevations so atmosphere = thicker
Jarosite
found on earth and on mars
Meridiani landing site on mars

[possible life?]
Bedrock is exposed in shallow craters, suggesting that this part of Mars is covered by only a very thin layer of windblown deposits -and it may be relatively easy to observe and analyze underlying rocks.

Rock outcrops or soil may contain insitu hematite -helping to explain its origin

Evidence for hematite in volcanic or hot-spring deposits
may be a great place to look for evidence of past life (e.g. fossils).
Mineral
IT MUST

1) Occurs naturally

2) Inorganic Solid

3) Possess orderly internal structure
[atoms must be arranged in a definite pattern]

4) Definite Chemical Composition
Rock
Solid aggregate (minerals joined so properties of each are maintained) mass of minerals
Mineral's ordered internal structure means...
every sample of the same mineral contains the same elements joined together in a pattern
Elements atomic structure:
nucleus contains protons = # of nuetrons

electrons surround nucleous
-located in shells (energy levels)
Atomic # determined by
# of protons

-atoms w/same atomic # = same element
Element
definition
collection of electrically neutral atoms with the same atomic number
Valence Electrons
Outermost electrons

-the ones involved in chemical bonding
Chemical Bonding
formation of a compound by combining 2+ elements

1.Ionic*
2.Covalent*
*usually occur together
3.Metallic
Ionic Bonding
gain/loose valence electrons to form ions
-after electron transfer, atoms no longer electrically neutral
-*aka* the attraction of oppositely charged ions to one another making a neutral compound

[Ions=atoms with an electrical charge
-anion (- atom)
-cation (+ atom)]

[ionic compounds=arrangement of oppositely charged ions
*internal atomic arrangement of minerals determined by size of ions]
Covalent Bonding
-atoms share electrons to gain neutrality
-covalent compounds stronger than ionic compounds
Metallic Bonding
Valence electrons free to migrate among atoms
-weaker & less common than covalent/ionic
mass #
Nuetrons + Protons
Isotope
atom with variation in mass #

-same # protons
-varying # nuetrons

**can have unstable nuclei that emit particles/energy
= RADIOACTIVE DECAY
[clock for earth's history]
Polymorph
Minerals with same chemical compositions but different cystalline structures

*2 minerals with same chemical comp can be joined together in different ways
==2 minerals w/different properties can have the same chemical comp.

-ex. diamond & graphite
{both polymorphs of carbon}
=both consist of carbon
=difference = how they were formed
[diamonds=compact, formed at greater depth
graphite=widely spaced, weakly held together]
*heating graphite under high pressure can make diamonds
*peanut butter in high pressure can make diamonds
The ordered atoms in a mineral form a particular crystalline structure.

The internal atomic arrangement is determined by:
-charges of the ions

-size of the ions involved
Physical properties of minerals
(list)
1) Crystal Form
2) Luster
3) Color
4) Streak
5) Hardness
6) Cleavage
7) Fracture
8) Specific Gravity
9) Other
CRYSTAL FORM
physical property
External expression of ordered internal arrangement of atoms

-crystal growth can be interrupted by not enough space or rapid heat loss

*not cleavage
LUSTER
physical property
appearance of mineral in reflected light

-1-metallic
(have appearance of metal, regardless of color)
-2-non-metallic

-other: oily, silky, earthy
COLOR
physical property
unreliable

highly variable for a given mineral due to slight variance in chemistry
STREAK
physical property
color of mineral in powdered form

-helpful in determining different forms of same mineral
HARDNESS
physical property
resistence of mineral to scratching

-determined by rubbing mineral with unknown hardness against one of known hardness

-compared on a standard scale:
MOHS SCALE OF HARDNESS
[10 minerals arranged in relative ranking from 1(softest-talc) to 10(hardest-diamond)]
CLEAVAGE
physical property
tendancy to break along bonds

-produces flat, shiny surfaces
-described by resulting shapes (# of planes, & angles joining planes)

*no cleavage called fracture
FRACTURE
physical property
absence of cleavage when mineral's broken

*quartz
SPECIFIC GRAVITY
physical property
ratio of weight of mineral to equal volume of water

-avg value = 2.7
-hefting mineral can work too
(comparing weight of mineral in hand to common rocks)
OTHER
physical properties
-magnetism
-reaction to hydrochloric acid
-malleability
-double refraction
(transparent mineral over printed material makes words appear twice)
-taste
-smell
-elasticity
Conchoidal Fracture
minerals that break into smooth curved surfaces resembling broken glass
Rock-Forming Minerals
common minerals that make up most of Earth's Crust

-8 main elements making up 98% of Crust
8 main elements in crust:
1)Oxygen
2)Silicon
3)Aluminum
4)Iron
5)Calcium
6)Sodium
7)Potassium
8)Magnesium
Silicates
-most important mineral group
-most of rock forming minerals are silicates
-abundant bc large amt of silicon & O2 in earth's crust
-basic building block =
SILICON-OXYGEN TETRAHEDRON molecule
===4 oxygen ions surrounding smaller silicon ion
Different Silicate Structures
(how silicon-oxygen tetrahedrons are joined)
-isolated tetrahedra
-ring structures
-single chain structures
-double chain structures
-sheet structures
-layered structures
-complex 3D structures
OLIVENE
silicate mineral
-no cleavage--conchoidal fracture
--forms small rounded crystals

-Crystalizes @ high temps

-Predominantly Iron & Magnesium (Fe-Mg Silicate)
---typical mantle mineral
-individual tetrahedra linked by Fe & Mg ions (single tetrahedra structure

-black->olive green color
-glassy luster
PYROXENE GROUP
silicate mineral
-single chain
-cleavage: 2 planes @ Right Angles
-Bonded by Fe & Mg

***AUGITE***
-black, opaque mineral
-one of the dominant minerals in Basalt
AMPHIBOLE GROUP
silicate mineral
-double chain
-cleavage: perfect cleavage; 124 & 56 degree angles
-Bonded by variety of ions

***HORNBLENDE***
-dark green-->black
-similer in appearance to augite (except for cleavage
MICA GROUP
silicate mineral
-sheet structures
-cleavage: sheet structures result in one direction of perfect cleavage (one plane)

***BIOTITE***
-common dark colored mica
-shiny, black
-iron rich

***MUSCOVITE***
-common light colored Mica
FELDSPAR GROUP
silicate mineral
-3D structure
-cleavage: perfect cleavage: 2 planes at 90 degrees
-most common mineral group

***Orthoclase (potassium feldspar)***
-contains potassium
-light cream -->salmon color
***Plagioclase (sodium & calcium feldspar)
-white->gray color
QUARTZ
silicate mineral
-3D structure
-NO cleavage
-consists entirely on silicon & oxygen
-light colored (varies)
-light weight
-**6 sided shape**
-develop pyramid shaped ends
Clay Minerals
(still silicates)
clay= general term to describe variety of minerals
-all have sheet structure
-originate from chemical weathering
important
NON-SILICATE MINERALS
-oxides
-sulfides
-sulfates
-native elements
-carbonates
-halides
-phosphates
CARBONATES
non-silicate minerals
primary constituents in limestone & dolostone

***Calcite
***Dolomite
Non-silicate minerals
w/ economic value
-Hematite
(oxide mined for iron ore)
-Halite
(halide mined for salt)
-Sphalerite
(sulfide mined for zinc)
-Native Copper
(native element mined for copper)
Igneous Rocks
form as molten rocks cool/solidify
Characteristics of Magma (molten rock)
-parent material of igneous rocks
-forms from partial melting of rocks in earth

*called lava only when reaches surface
Extrusive / Volcanic Rocks
rocks formed from lava at surfacee
Intrusive / Plutonic Rocks
rocks formed from magma that crystallizes at depth
[ex. Granite]
3 Components of Magma
1)MELT: liquid portion (mobile ions of elements from crust-mostly silicon & oxygen)
2)SOLIDS:(if any)silicate minerals that have already crystallized
3)VOLATILES:gases dissolved in melt [H20, carbon dioxide, sulfur dioxide]
Crystallization of Magma
as magma cools ions in the melt loose their mobility & arrange themselves in an ordered crystalline structures
(normally O2 and silicon link together first
Igneous Rocks are Classified by
1. Texture
(size/shape/arrangement of interlocking crystals)
2. Mineral Composition
Factors Contributing to Texture of Igneous Rocks
1) the rate magma cools
-slow cooling = fewer & Larger crystals
-fast rate = many small crystals
-very fast rate = glass (no time for ions to arrange=unordered ions=glass)

2) amount of silica present

3) amount of dissolved gases in the magma
Types of Igneous Textures
1)Alphanitic (fine grained)
2)Phaneritic (coarse grained)
3)Porphyritic
4)Glassy
5)Pyroclastic (fragmental)
6)Pegmatitic
APHANITIC
igneous texture
-fine grained texture
-rapid rate of cooling of lava or magma
-microscopic crystals
-can contain Vesicles [holes from gas bubbles]
PHANERITIC
igneous texture
-coarse grained texture
-slow cooling
-crystals identified w/o microscope
-ex GRANITE
POPHYRITIC
igneous texture
-minerals form at different temperatures & different rates
-Large crystals [PHENOCRYSTS] are embedded in a matrix of smaller crystals [GROUNDMASS]
GLASSY
igneouos texture
-very rapid cooling of igneous rock
-OBSIDEAN=resulting rock (arrowheads)
PYROCLASTIC
igneous texture
-various fragments ejected during violent volcanic eruption
-superheated/superfast flows
-appear similar to sedimentary rocks
PEGMATITIC
igneous texture
-exceptionally coarse grained
-forms in late stages of crystallization of granitic magmas
-VERY Large crystals
Dark (ferromagnesian*) Silicate Minerals that Igneous Rocks are Composed Of
-olivene
-pyroxene
-amphibole
-biotite mica

*ferromagnesian=contain Fe or Mg in structure & are heavier
Light Silicate Minerals that Igneous Rocks are Composed of
-Quartz
-Muscovite Mica
-Feldspars


*not much Fe & Mg
Granitic v Basaltic Composition of Igneous Rocks
1)Granitic:
-light colored silicates
-"felsic" (feldspar & silica in composition)
-high amounts of silica
-major part of earth's crust

2)Basaltic
-composed of dark silicates & feldspar
-"mafic" (magnesium & ferrum {iron} in composition)
-more dense than granitic
-make up ocean floor & many volcanic islands
GRANITE
igneous rock
-Granitic (felsic)
-phaneritic
-65% quartz
-25% feldspar
-abundant
-associated with mountiain building
-"granite" covers many different mineral compositions

-pink & coarse-grained
RHYOLITE
igneous rock
-GRANITIC (Felsic)
-extrusive equivalent to granite [granite that made it to the surface]
-alphanitic texture
-less common than granite
-phenocrysts (large crystal embedded in matrix can be quartz or feldspar)
BASALT
igneous rock
-BASALTIC (mafic)
-volcanic origin
-alphanitic texture
-composed mainly of pyroxene & plagioclase feldspar
-most common extrusive igneous rock
GABBRO
igneous rock
-BASALTIC (mafic)
-intrusive equivalent to basalt
-phaneritic texture of pyroxene & plagioclase
-makes up a lot of oceanic crust
OTHER COMPOSITIONAL GROUPS OF IGNEOUS ROCKS
(other than granitic & basaltic)
1) Intermediate (Andesitic) Composition
-25+% dark silicate minerals
-associated with explosive volcanic activity

2)ULTRAMAFIC Composition
-rare
-high in Fe & Mg
-composed entirely of ferromagnesium silicates
ANDESITE
igneous rock
-INTERMEDIATE (andesitic) composition
-volcanic origin
-alphanitic texture
-resembles rhyolite
DIORITE
igneous rock
-plutonic (deep magma origin) equivalent to andesite
-coarse grained
-intrusive
-made up of intermediate feldspar & amphibole
Silica Content Changes Magma's Behavior

GRANITIC V BASALTIC MAGMA
1)Granitic Magma
-high silica content==
==more viscous (=thicker)==
==usually lose mobility before reaching surface
==tend to produce large plutonic structures (rocky mtn nat'l park, pikes peak)
-still liquid at low temps (700 C)
-goes BOOM when erupts
-[Yellowstone]

2)BASALTIC MAGMA
-low silica content
-fluid-like behavior
-crystallizes at high temps
-Gurgles when it erupts
-[Hawaii]
OBSIDIAN
igneous rock
-GRANITIC (felsic)
-dark colored
-glassy texture
-usually when lava's put out quickly
PUMICE
igneous rock
-GRANTIC (felsic)
-volcanic
-glassy texture
-frothy appearance (extrusive foam)
-usually found with obsidian
-formed when large amts of gas escape through lava (generates gray frothy mass)
-many samples float in water
PYROCLASTIC ROCKS
composed of fragments ejected during volcanic eruption
-2 types of pyroclastic rock:

1)Tuff
-ash sized fragments

2)Volcanic Breccia
-particles larger than ash
Geothermal Gradiant
Change in Temperature with Depth

-rate of temp change avgs at 20-30 C per Kilometer
Origin of Magma
originates by rocks melting in earth's mantle
-since mantle is made of mostly solid rock, magma is formed when rocks are raised above their melting point.

-rocks are raised above their melting point by:
1)added heat
2)decrease in pressure
3)introduction of volatiles
Heat's role with Magma
-rocks in lower crust/upper mantle are near melting points
-rocks lowering into mantle or heat rising from mantle helps induce melting
Pressure's role with Magma
-melting occurs at higher temperature due to pressure

-when pressure drops enough "Decompression Melting" is triggered
==[rock can ascend into lower pressure areas]===responsible for magma at plate bounderies
Volatile's role with Magma
volatiles (gas components of magma)---USUALLY WATER---
Cause rocks to melt at LOWER temperature

-effect of volatiles magnified by increasing pressure

-volatiles play important role where cool slabs of oceanic crust lower into mantle
Melting & Crystallization of Magma temperature range
Both span a great temperature range of about 200 C
Processes Responsible for Different Magma Compositions

(and thus wide variety of igneous rocks)
1)Magmatic Differentiation
2)Assimilation
3)Magma Mixing
4)Partial Melting
MAGMATIC DIFFERENTIATION

{changing magma composition}
**WHEN 2+ SECONDARY MAGMAS FORM FROM A SINGLE PARENT MAGMA**


because minerals crystallize at different temps
a seperation of solid and liquid in magma can occur
-this happens when earlier formed crystals are denser than the liquid magma

-the solid crystals sink to the bottom of magma chamber
-when the remaining melt solidifies it will have a much different chemical composition from the first solid crystals & the parent magma
ASSIMILATION

{changing magma composition}
**CHANGING A MAGMA'S COMPOSITION BY THE INCORPORATION OF FOREIGN MATTER (surrounding rock bodies) INTO A MAGMA**
MAGMA MIXING

{changing magma composition}
**TWO BODIES OF MAGMA INTRUDING ONE ANOTHER**

-2 chemically distinct magmas can produce a composition much different from the either original magma
PARTIAL MELTING

{changing magma composition}
**INCOMPLETE MELTING OF ROCK**

since the melting of rocks has such a great temp range
minerals with lowest melting temps are first to melt.
-as melting continues magma approaches the composition of the rock it was derived from
-most of the time complete melting, however, does not occur
Formation of Basaltic Magmas
From Partial Melting
-most originate from partial melting of ultramafic rock in mantle
-form at:
(1)mid-ocean ridges by decompression melting
(2)subduction zones
(water driven from descending slab of oceananic crust promotes partial melting
-as basaltic magma migrates up pressure decreases & reduces melting temperature (magma doesn't crystallize @ depth)
-outpourings are common on earth's surface
Formation of Andesitic Magmas
From Partial Melting
-interactions between basaltic magma & silica-rich parts of earth's crust generate andesitic magma
(ex. basaltic magma migrates up & melts/assimilates crustal rocks it ascends through)

-Can also form from magmatic differentiation
(as basaltic magma solidifies the silica-poor minerals crystallize first.
=the remaining melt (now enriched in silica) has an Andesitic Composition
[secondary magma]
Formation of Granitic Magmas
From Partial Melting
-likely to form as the end product of the crystallization of andesitic magma (magmatic differentiation)
-or partial melting of silica rich continental rocks
Factors that determine violence/explosiveness of Volcanic Eruption
The viscosity determines the violence which is determined by:

1)Composition of Magma
2)Temperature of Magma
3)Dissolved Gasses in Magma

More Visous = More Explosive
Viscosity
measure of material's resistence to flow
[higher viscosity->difficult to flow]

Factors Affecting Viscosity
1)TEMPERATURE:
higher temp = less viscous = more fluid (like syrup)
2)COMPOSITION:
-higher silica = more viscous (ryolite)
*more silica means impeded flow bc silica's in chain structures
-lower silica = lower viscosity [more fluid] (eg mafic lava{basalt})
3)DISSOLVED GASSES:
-volatiles (dissolved gas in magma) increase the fluidity of magma (lower viscosity)
-gases expand as magma nears earth's surface due to decreasing pressure
-violence of eruption depends on how easily gases escape from magma
How do Dissolved Gasses affect an eruption
-volatiles (dissolved gas in magma) increase the fluidity of magma

IN addition
-more gas= more force to propel lava...
-before an eruption volatiles (gaseous component of magma) migrate up and accumulate near top of magma chamber
=upper portion of magma is enriched in gases
=gas-charged magma moves from chambe and risses through vent
=as nears surface pressure is reduced
=gases expand
=dissolved gasses release suddenly (like pop can)

*fluid basaltic magmas allow gasses to rise with ease. produce lava fountains. *calm eruptions*

*more viscous magmas = much more explosive.
prior to eruption magmatic differentiation leaves iron-rich minerals behind & upper portion of magma is enriched in silica & dissolved gasses.
when magma in upper portion is released, pressure drops on magma below and explosion is followed by emission of degassed lavas.
*ryolite or andesite*
*yellowstone & mt st helens go BOOM*

------dissolved gasses=1-6% of magma----mostly H20 & Carbon Dioxide
Types of Basaltic Lava Flows
1) Pahoehoe Flows
-smooth skin that wrinkles
as still molten subsurface continues moving
-twisted ropey texture
-(can make lava tubes)
-hotter, richer in gasses, faster than aa flows

2)Aa Flows
-rough jagged blocky texture
-pahoehoe can turn into Aa
Pyroclastic Material
propelled blobs of lava ejected from volcano ("fire fragments")

Types:
1)Ash & Dust
-fine glassy fragments
2)Pumice
-pourous rock from "frothy" lavas
3)Lapilli
-walnut sized
4)Cinders
-pea sized

*Particles Larger than Lapilli*
5)Blocks
-Hardened/cooled lava
6)Bombs
-ejected as hot lava balls
-~10cm long
Crater
(volcano terms)
steep walled depression at the summit
-less than 1 km in diameter
-smaller than a caldera
Caldera
(volcano terms)
very large circular depression at summit
-larger than 1 km in diameter
-its a collapse structure
-produced by a collapse that followed a massive eruption
Vent
(volcano terms)
the opening of a pipe that connnects to a magma chamber
3 Types of Volcanos
1) Shield Volcanos
2) Cinder Cones
3) Composite Cones
Shield Volcanos
-broad, dome-shaped
-made up of Basaltic Lava
-covers large area
-produced by mild eruptions of mass amts of lava
-ex. Mauna Loa (hawaii)
-Olympus Mons (on mars = huge shield volcano
-calderas common to mature shield volcanos
-once a shield eruption volcano is well established most of lava flows through lava tubes -> increase the distance lava can travel before it solidifies
Cinder Cone
Volcanos
-Built from ejected lava fragments (mainly cinder-sized)===>>made of pyroclastic material
-steep slope
-have large deep craters
-usually product of single eruptive episode
-usually small
-usually occur in groups
Composite Cone
Volcanos

(Stratovolcano)
-potentially dangerous
-most located in "ring of fire" which rims the PACIFIC OCEAN
-large, classic shape (thousands feet high, miles-wide base)
-due to thick lava that travel short distances
-made up of interlayed layers of lava flows and layers of pyroclastic debris
-most violent volcanos
-often produce nueé ardente
[the most destructive form of pyroclastic flow]
-Can produce a LAHAR [a volcanic mudflow]
-ex. Mt St Helens
nueé ardente
-the most destructive pyroclastic flow {flows of a mix of hot gases, ash, & large rock fragments}

-the bottom portion is suspended by jets of buoyant gases passing up through flow
-trapped air provides buoyancy
===travels in nearly frictionless enviro
=====can race down steep volcanic slopes
==go up to 200km/hr

**produced by composite cone volcanos**
Lahar
a mudflow occuring when volcanic debris becomes saturated with water

-can be triggered by ice melting when volcano erupts

**caused by composite cone volcanos**
pyroclastic flows
explosive mix of rock glass & heat
-only with felsic & intermediate magma
-ash, pumice & other fragments propelled at high speed
Crater Lake formed from a Caldera
the magma chamber is partially emptied
-the dome part of volcano collapses
-forms crater :)
The greatest volume of lava is extruded by:
FISSURE ERUPTIONS
fissure eruptions
basaltic lava is extruded from fractures in crust (called FISSURES)
-some can flow far away from source (*flood basalts*) & cover huge areas
-occur worldwide
-ex. Columbia Pateau
----Snake River Plain in
Lava Domes
(volcanic landform)
bulbous mass of solid lava
-from explosive eruptions of gas rich magma (silica rich)

[late stages andesitic composite cones... looks like bulge inside of top of volcano]
Volcanic

Pipes v Necks
PIPES:
-short channels connecting magma chamber to surface

NECKS:
-resistent vents left standing after erosion has removed volcano
(ex devils tower in wyoming)
Dikes
Sills
Lacolliths
are all
intrusive igneous features
Intrusive or Extrusive Igneous features?
Dikes
-a crack that cross cuts rocks
-sheetlike injection
-occurs when magma's injected into fractures
-look like a wall if material around it erodes
-"injection into a fracture"
-**vertical**
Sills
-formed when magma's injected sideways into rock layers
-only form at shallow depths where pressure from rocks on top is low (so they can be lifted so sill can flow inbetween)
-"injection into a bedding plane"
-**horizontal**
Lacollith
-occur when magma's intruded between layers near the surface
-magma generating lacollith more viscous (less fluid) & collects, pushing overhead rocks upward
-lens/mushroom shaped mass
-"arches overhead strata upward"
-similar to sill
Granite is Usually Found in
Continents
Oceans or Continents?
Basalt Usually found in
BOTH oceanic and continental settings
Oceans or Continents?
Most Volcanos are Located
Within / Near Ocean basins